Steve Cecil, Vicki Yearick
AnalytiX Volume 8 Issue 2
Detailed hydrocarbon analysis (DHA) applications are widely used in the petroleum industry to characterise light petroleum fractions with boiling points up to 450 °F/225 °C. These applications comply with ASTM methods D5134, D6729, D6730 and D6733 which use single-column gas chromatography (GC) to group the hydrocarbon components by structure.
DHA is applied to petroleum streams comprising naphtha, alkylate, reformer feed, reformate, isomerate, gasoline and compressed liquids. DHA characterisation of these streams is based on the Kovats Index, and differentiates the composition and concentrations into five groups that are collectively called PIANO:
Paraffins, Isoparaffins, Aromatics, Naphthenes, and Olefins.
Precise calibration of the chromatographic system is critical for running successful DHA applications. Calibration utilises a set of six complex, quantitative analytical standards known as the PIANO standards. These standards are diffi cult for most laboratories to prepare due to their complexity and the lack of commercial sources of the many branched-chain hydrocarbons in the mixtures.
To facilitate DHA analysis, Sigma-Aldrich now offers ALPHAGAZ™ PIANO standards as kits and individual mixtures. The kit includes a 139 component quantitative multi-group PIANO mix, plus the five individual quantitative PIANO group mixes. ALPHAGAZ PIANO standards are accurately prepared by weight to three decimal places. Each mixture is shipped with a comprehensive analytical data sheet listing components by weight percent, mole percent, liquid volume percent, retention times and retention indices for each component. A chromatogram of each mixture is also provided. The standards are supplied in crimp-top vials with hole caps and septa.
Utilising these six high-quality analytical standards will ensure the GC system is optimised for proper performance of the DHA analyser. These standards should also be used to perform routine quality assurance checks on the GC system. Checking the system regularly with the Supelco 139-component PIANO mix will reveal the need for maintenance of the GC system, including when it is time to replace the column.
In addition to the standards, we also offer an ideal, petroleum-specific GC column for DHA analysis, the 100-metre Supelco Petrocol™ DH. This column is specifi cally manufactured for the analysis of complex hydrocarbon mixtures and is ideally suited for DHA systems.
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